1). Field of the Invention
This invention relates to a method and apparatus for bonding a wire to a bond pad on a device, such as an electronic or a photonic device.
2). Discussion of Related Art
Electronic and photonic devices usually have a number of bond pads on upper surfaces thereof that are connected to bond pads on package substrates or other devices for purposes of providing electronic signals to and from the electronic or photonic devices.
A common technique for interconnecting such bond pads is wirebonding. A portion of a wire is held against a bond pad, and ultrasonic energy is provided through an ultrasonic bond head to an interface between the portion of the wire and the bond pad. Such energy by itself is usually insufficient to fuse the wire to the bond pad. The electronic device is usually heated to approximately 180° C. by a substrate workholder during the bonding process. Heat energy from the workholder supplements the ultrasonic energy, and the combination of the heat energy and ultrasonic energy is sufficient to fuse the wire to the bond pad.
Several electronic and photonic devices will be damaged at high temperatures, and often require processing conditions much below the 180° C. to which a device has to be heated for purposes of ultrasonic bonding. The maximum temperatures for some integrated circuit packages having certain thin films may, for example, be below 100° C. Ultrasonic bonding at such low temperatures is usually not possible. Ultrasonic bonding of gold wires to aluminum-capped wirebond pads at temperatures below 125° C., for example, is generally not possible.